The present invention relates to a system and method for recording and/or reproducing signals with respect to parallel tracks of a recording medium and more specifically, to such systems utilizing a prerecorded track as a reference for positioning a signal transducer to accurately follow predetermined parallel paths.
In the art of recording information signals on a medium, such as in magnetic or optical recording, there is a trend to increase recording density. This can be accomplished by reducing the recording track width as well as the width of a guard band separating adjacent tracks to minimum. When recording or reproducing such narrow tracks on or from a medium, it is necessary to accurately position the transducer so that it accurately follows a desired path. During recording of information signals on such narrow tracks it is important to provide parallel tracks with each other as accurately as possible in order to utilize the entire surface of the recording medium without overlapping adjacent tracks. During reproduction, it is equally important to precisely position the playback transducer over the recorded tracks and to maintain it in registration with these tracks, otherwise valuable information content may be lost.
Previous developments in the art of reproducing magnetically recorded signals yielded a large variety of track following mechanisms, also referred to as automatic tracking systems. These systems generally utilize a magnetic transducer mounted on a support mechanism whose position may be adjusted with respect to the magnetic medium transport. For example piezoelectric bender or voice-coil actuators have been utilized as transducer positioning means. During playback these tracking systems sense a deviation of the transducing gap from the center of a recorded information signal track. An error signal indicating such deviation is applied to a servo mechanism which, in turn moves the transducer to the desired position. However, these known tracking systems are generally useful only during playback.
As previously indicated it is desirable to record information signals on closely spaced narrow tracks parallel to each-other with a high degree of accuracy and as "straight" as possible, while maintaining a narrow guard band between the tracks. Known prior art longitudinal recording systems utilize the edge of a magnetic medium, for example tape, as a reference for recording parallel longitudinal tracks. In known helical tape recorders, it is also important to accurately guide the tape edge, for example, by known mechanical guiding means, such as band guides or a machined ridge on the drum. Such tape edges are, however, an unreliable reference because they often become damaged, for example, stretched, curled or chopped by improper handling or changed environmental conditions. In addition, magnetic tape edges are often cut in a slightly wavy pattern, generally referred to as having slitting errors caused by the runout of rotating-disc cutters used to cut tape webs to a desired width.
Consequently, in systems where the accuracy of obtaining parallel recorded tracks depends on the mechanical condition of tape edges, gross tracking errors may be introduced when the reference edges are imperfect.
There are also known systems which utilize tracks recorded on the medium as a reference for transducer positioning. In these systems, the position sensing is obtained by transducing channels which are an integral part of the moveable multichannel transducer structure and have to be moved therewith. The position sensing channels contribute to the relatively large size and thus mass of the moveable multichannel transducer. This increases the response time for moving the transducer to a desired position. Another disadvantage is that when it is required of the transducer to follow in sequence a plurality of spaced parallel paths on the medium a plurality of separate reference tracks must be provided, one for each path. These reference tracks significantly reduce the space on the medium which would be otherwise available for recording of useful information signals, thereby reducing the overall obtainable recording density.